The present invention relates generally to fluid filters and, particularly, to a replaceable type oil filter for use in the lubricating systems of internal combustion engines. More specifically, the present invention relates to an oil filter of the above-described type which is provided with an additive body located within the filter enclosure and adapted to dissolve over the service life of the oil so as to replenish additives normally provided in modern engine lubricating oils. Typically, such additives which become depleted over the service life may consist of viscosity index improvers, anti-oxidents and anti-wear - anti-corrosion compounds. A more detailed description of the general type of filter unit to which this specification is directed is disclosed in U.S. pat. application Ser. No. 564,111, filed Apr. 1, 1975.